1. Field of the Invention
The present invention relates to a battery pack in which a protection circuit and a protection element are attached to a unit cell and the protection circuit and the protection element are housed within a cover.
2. Description of Related Art
In recent years, battery packs have been increasingly miniaturized, and many battery packs use a resin cover or a resin, frame-shaped case as an exterior component of the battery packs. A protection circuit that prevents overcharge, overcurrent, overdischarge, or the like is mounted on the battery packs. A resin internal frame is used to support the protection circuit.
FIGS. 7A and 7B are perspective views showing an example of a conventional battery pack. The perspective view of FIG. 7A shows the entire battery pack, and FIG. 7B is an enlarged view of portion C of FIG. 7A. A resin internal frame 101 is attached to a unit cell 100. A protection element (not shown) is housed within the interior of the internal frame 101, and the internal frame 101 supports a protection circuit 102.
The internal frame 101 is provided with a fixing claw 103, and a cover 104 is provided with a hole 105. The cover 104 is fixed to the internal frame 101 by engaging the fixing claw 103 of the internal frame 101 with the hole 105 of the cover 104.
Moreover, various types of configurations in which the cover is attached to a component corresponding to the internal frame are described in JP 2005-142153A, JP 2006-164601A, and JP 2006-302662A. JP 2005-142153A describes a structure in which an engaging claw formed on a frame portion enclosing a unit cell is engaged with an engaging hole formed in a cap portion (a cover), thereby attaching the cover to the frame portion. JP 2006-164601A describes a structure in which a fitting projection formed on a board holder is engaged with a fitting recess formed in an exterior case (a cover), thereby attaching the exterior case to the board holder. JP 2006-302662A describes a structure in which a screw is passed through a hole formed in a cover, and the screw is then threaded into a nut portion formed on a terminal portion of a unit cell, thereby attaching the cover to the unit cell.
On the other hand, in some structures for attaching the cover to the unit cell, integral molding is used rather than engagement to attach the cover to the unit cell so that the mechanical strength of the battery pack is increased.
However, with a (snap-fit) structure as described in FIGS. 7A and 7B and JP 2005-142153A and JP 2006-164601A in which a fitting projection formed on the internal frame is engaged with a fitting recess (or a hole) formed in the cover, there is a possibility that the engagement may be cancelled and the cover may be dislodged when the battery pack is subjected to an impact due to, for example, dropping. Thus, this structure is disadvantageous for increasing the impact resistance.
Moreover, a structure as described in JP 2006-302662A in which the cover is attached to the unit cell by screwing and a structure in which the cover is attached to the unit cell by integral molding require a larger number of components and a larger number of steps of the manufacturing process. Thus, these structures are disadvantageous in terms of cost.